feat(compliance): improve compliance

ts/einvoice.ts

@@ -365,7 +365,7 @@ export class EInvoice implements TInvoice {
    * Maps this EInvoice instance to a TInvoice
    */
   private mapToTInvoice(): TInvoice {
-    return {
+    const invoice: any = {
       type: 'accounting-doc',
       accountingDocType: this.accountingDocType,
       accountingDocId: this.accountingDocId || this.id,
@@ -394,6 +394,13 @@ export class EInvoice implements TInvoice {
       relatedDocuments: this.relatedDocuments,
       printResult: this.printResult
     };
+    
+    // Preserve metadata for enhanced spec compliance
+    if ((this as any).metadata) {
+      invoice.metadata = (this as any).metadata;
+    }
+    
+    return invoice;
   }
 
   /**